On Thu 15-12-22 09:33:54, Mathieu Desnoyers wrote:
> On 2022-12-15 02:51, Michal Hocko wrote:
[...]
> > Btw. looking at the code again it seems rather pointless to duplicate
> > the policy just to throw it away anyway. A slightly bigger diff but this
> > looks more reasonable to me. What do you think? I can also send it as a
> > clean up on top of your fix.
>
> I think it would be best if this comes as a cleanup on top of my fix. The
> diff is larger than the minimal change needed to fix the leak in stable
> branches.
>
> Your approach looks fine, except for the vma_policy(vma) -> old change
> already spotted by Aneesh.
This shouldn't have any real effect on the functionality. Anyway, here
is a follow up cleanup:
---
>From f3fdb6f65fa3977aab13378b8e299b168719577c Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@xxxxxxxx>
Date: Thu, 15 Dec 2022 15:41:27 +0100
Subject: [PATCH] mm/mempolicy: do not duplicate policy if it is not applicable
for set_mempolicy_home_node
set_mempolicy_home_node tries to duplicate a memory policy before
checking it whether it is applicable for the operation. There is
no real reason for doing that and it might actually be a pointless
memory allocation and deallocation exercise for MPOL_INTERLEAVE.
Not a big problem but we can do better. Simply check the policy before
acting on it.
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
mm/mempolicy.c | 28 ++++++++++++----------------
1 file changed, 12 insertions(+), 16 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 02c8a712282f..becf41e10076 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1489,7 +1489,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
- struct mempolicy *new;
+ struct mempolicy *new, *old;
unsigned long vmstart;
unsigned long vmend;
unsigned long end;
@@ -1521,31 +1521,27 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
return 0;
mmap_write_lock(mm);
for_each_vma_range(vmi, vma, end) {
- vmstart = max(start, vma->vm_start);
- vmend = min(end, vma->vm_end);
- new = mpol_dup(vma_policy(vma));
- if (IS_ERR(new)) {
- err = PTR_ERR(new);
- break;
- }
- /*
- * Only update home node if there is an existing vma policy
- */
- if (!new)
- continue;
-
/*
* If any vma in the range got policy other than MPOL_BIND
* or MPOL_PREFERRED_MANY we return error. We don't reset
* the home node for vmas we already updated before.
*/
- if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) {
- mpol_put(new);
+ old = vma_policy(vma);
+ if (!old)
+ continue;
+ if (old->mode != MPOL_BIND && old->mode != MPOL_PREFERRED_MANY) {
err = -EOPNOTSUPP;
break;
}
+ new = mpol_dup(old);
+ if (IS_ERR(new)) {
+ err = PTR_ERR(new);
+ break;
+ }
new->home_node = home_node;
+ vmstart = max(start, vma->vm_start);
+ vmend = min(end, vma->vm_end);
err = mbind_range(mm, vmstart, vmend, new);
mpol_put(new);
if (err)
--
2.30.2
--
Michal Hocko
SUSE Labs
